High-speed networks are continually evolving. The evolution includes a continuing advancement in the operational speed of the networks. The network implementation of choice that has emerged is Ethernet networks physically connected over unshielded twisted pair wiring. Ethernet in its 10BASE-T form is one of the most prevalent high speed LANs (local area network) for providing connectivity between personal computers, workstations and servers.
High-speed LAN technologies include 100BASE-T (Fast Ethernet) and 1000BASE-T (Gigabit Ethernet). Fast Ethernet technology has provided a smooth evolution from 10 Megabits per second (Mbps) performance of 10BASE-T to the 100 Mbps performance of 100BASE-T. Gigabit Ethernet provides 1 Gigabit per second (Gbps) bandwidth with essentially the simplicity of Ethernet. There is a desire to increase operating performance of Ethernet to even greater data rates.
FIG. 1 shows a block diagram of an Ethernet system. This system includes switches 110, 115, a server 120, a set of blade servers 140, and a personal computer 145. Each of the Ethernet devices 110, 115, 120, 140 includes Ethernet transceivers 130 which enable transmission of Ethernet signals between the devices 110, 115, 120, 140. The signal transmission is over Ethernet transmission channels that are provided by cables and connectors, such as cable 150 and connector 155.
Cables and connectors located proximate to each other can suffer from coupling of signals from one cable and connector to another cable and connector. The coupling is referred to as crosstalk, and is undesirable because crosstalk signals can interfere with intended transmission signals. Crosstalk signals become more prominent as transmission frequencies increase in transmission frequency. Therefore, as Ethernet system progress to 10GBASE-T, crosstalk signals become a greater problem.
One way to reduce the effects of crosstalk is to reduce the signal level of transmission signals. Lower amplitude transmission signals result in lower amplitude crosstalk, and therefore, cause less interference. However, transmission signal amplitude reduction can cause other problems. The transmission can be made unreliable by reducing the transmission signal amplitude because the SNR (signal to noise ratio) is typically decreased.
One proposed method of reducing transmission signal amplitude to minimize crosstalk is to determine the worst case crosstalk within a network. The signal amplitude of all transmitters within the network is reduced until the worst case crosstalk meets a predetermined threshold. The amplitudes of transmission signals of the entire network are reduced to the worst case, to ensure that the crosstalk of the entire network meets the crosstalk threshold. This solution is inefficient, however, because the transmission channels (cables) of most of the network can have much greater transmission signal amplitudes without causing crosstalk problems. As a result, data transmission within the system suffers excessively.
It is desirable to have a system, apparatus and method of adjusting transmission signal amplitudes (power backoff) of transmitters of a network to provide a desired level of crosstalk within the network. The power backoff is desirably adjusted to allow the transmission signal amplitude to be as great as possible while still meeting the desired crosstalk threshold.